Process to create artificial nerves for biomechanical systems using optical waveguide network

ABSTRACT

A device for responding to touch discrimination comprises an array of optical fibers distributed over a supporting substrate and a UV holographic processor is connected to the fibers rendering the fibers capable of responding to touch discrimination and location identification. The substrate is an artificial limb having the array of optical fibers thereon that have a density substantially similar to that of the human body. Wavelength comparators are associated with the optical fibers, the wave length comparators providing numerous sensing locations in a single fiber strand as part of a complete fiber optic network for mechanical actuation and sensory feed back.

RELATED PATENT APPLICATION

This application is a continuation-in-part of U.S. Pat. No. 09/812,939filed on Mar. 27, 2001 now abandoned and claims benefit of priorityunder 35 U.S.C. §119 to provisional patent application Ser. No.60/192,372, filed Mar. 27, 2000.

FIELD OF THE INVENTION

The present invention is a process for creating a network of artificialnerves for biomechanical systems. More particularly, the presentinvention is directed to an artificial nervous system design thatemploys ultra-fine registration of sensory locations in opticalwaveguide media using metrological tools that permit either DenseWavelength Division Multiplexing (DWDM), incorporated in its entiretyherein by reference, or Dense Time Division Multiplexing (DTDM) of thereturn signals corresponding to sensory input.

BACKGROUND OF THE INVENTION

There is a serious medical and psychological need for the restoration ofsensation for those who have lost sensation due to injury or othermishaps. This patent addresses architectures and techniques forproducing sensors and biomechanical structures that could meet theseneeds. As one example of its use, upon performing the processes outlinedin this patent, one possible resulting device could ultimately allow anindividual who has need of a prosthetic device to be outfitted with aunit which will give the sensation of ‘touch and feel’. Specificallyprocessed optical waveguides from this invention can be incorporatedinto prosthetic devices or into other human/animal sub-systems and willfunction as synthetic nerves. Photo-induced holograms within thesewaveguides act as sensory mechanisms that give intelligent feedbackinformation to the host via embedded microprocessors for mechanicalactuation. In the human body, the central nervous system is organized ina hierarchical arrangement with each level having a certain task inmotor functioning. Neurons function in the perceptions of the initialstimulus carrying their chemical messengers along a network to thebrainstem, which also forms a pathway that descends into the spinalcolumn, to influence motor movement.

SUMMARY OF THE INVENTION

One aspect of the current invention establishes an interface in thevicinity of the truncated portion of the missing limb using specificsites that are known to be sensitive to external stimuli. Opticalsignals relating strain levels to ‘touch responses’ are converted intomodulated electrical impulses encoded according to the location of itsorigination signal and its corresponding signal amplitude. It is assumedthat some of these signals will travel the same pathways and that thefinal decoding will be accomplished by training during therehabilitation phase of the patient. Thus similar, externally attached,devices may be used for persons not necessarily missing a limb toaccomplish other sensory functions and, with the use of biologicallycompatible waveguide materials, such as certain photopolymers, insertionof internal nerves units will be accomplished.

Hill et at. K. O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki,“Photosensitivity in optical fiber waveguides: Application to reflectionfilter fabrication”, Appl. Phys. Lett., 32 (10), pp. 647–9, 1978. firstreported and produced a Bragg reflection grating using a longitudinallaunch technique. Following Hill's initial work, D. R. Lyons repeatedtheir results using the 488 nm line of an argon-ion laser and shortlythereafter fabricated the first transverse diffraction gratings.Consequently, he established transverse holographic experimental setupswith several UV laser sources using the novel approach of sideillumination of the fiber. D. R. Lyons, Internal Reports, LawrenceLivermore National Laboratory, Livermore, Calif., 1986–1990.

This approach demonstrated substantial improvement in the fabrication ofBragg gratings and had several advantages including lower powerrequirements to produce interference gratings, the ability to createhighly wavelength selective modal discriminators, the capability ofwriting holographic patterns at practically any wavelength above thewriting laser wavelength, and the inherent facility to write a largenumber of gratings into a single fiber. Hill's initial method onlypermitted a single grating to be written in the fiber at a singlewavelength. Later studies have been successful in replicating thefabrication of transverse Bragg gratings and have led to a number ofuseful applications. G. Meltz, W. W. Morey, and W. H. Glenn, “Formationof Bragg gratings in optical fibers by a transverse holographic method,”Opt. Lett., 14 (15), 823, (1989). J. D. Prohaska, B. Chen, M. H. Maher,E. G. Nawy, and W. W. Morey “Fiber Optic Bragg Grating Strain Sensor inLarge Scale Concrete Structures”, SPIE vol. 1798 Fiber Optic SmartStructures and Skins, (1992).

The current invention allows the construction of distributed sensingnetworks, based upon Bragg reflection fiber optic filters in a denselypacked, single fiber format for distributed strain measurements. Thecurrent invention also incorporates feedback data from a number ofstrain and temperature sensors that have the advantage ofpre-registration of its sensing locations using the techniques devisedin U.S. Pat. No. 5,552,882, incorporated herein in its entirety byreference. D. R. Lyons, “Optical Electronic Multiplexing ReflectionsSensor System,” U.S. Pat. No. 5,191,458, (March 1993).

The ability to produce grating patterns and the nonlinear mechanismsdescribing their formation form the basis for ideas involving the use ofthe length limited Bragg reflection filters as well as their underlyingproperties. The fabrication of distributed fiber optic sensors reliesupon the photorefractive properties of germanium doped silica fibers. Inparticular, the wavelength region from 170 to 400 nm possesses strongabsorption bands for Ge doped optical fiber. M. Josephine Yuen,“Ultraviolet Absorption Studies of Germanium Silicate Glasses”, Appl.Opt., 21 (1), 136 (1982). For certain optical configurations thesegratings act independently to reflect a predetermined number ofwavelengths at preset static amplitudes. The dynamic amplitude and thewavelength of the reflections are proportional to the induced strainsand strain locations respectively.

An example readout method of involves the illumination of a reflectionfilter with an SLD (superluminescent laser diode) light source anddetection of the back reflected signals at the Bragg wavelengths, FIG.4. An improved version of this setup incorporates a tunable laser withwavelength scanning capabilities (also shown in FIG. 4). The spectralcharacteristics of a transverse holographic grating are derived fromcoupled mode theory. Forward and reverse traveling wave formulationsimply that the reflectivity at the Bragg wavelength is given by R=tanh²ξwhere

$\xi = {{\pi\;\frac{nL}{\lambda}\left( \frac{\Delta\; n}{n} \right){\eta(V)}\mspace{14mu}{with}\mspace{14mu}\eta} \approx {1 - {\frac{1}{V^{2}}\mspace{14mu}{\left( {V \geq 2.4} \right).}}}}$η is the fraction of integrated fundamental mode intensity in the core,with typical line widths of 20 to 40 GHz.

In the implementation of the current invention, the diagram of FIG. 3assumes that a first generation ‘intelligent arm’ will only addresssensations from its exterior. However, this technology or some valiantof it will ultimately be used to address interior portions with possibledirect interfaces with living tissue through the use of more inertmaterials.

In view of the aforementioned purposes of the present invention, ametrological standard (referred to in U.S. Pat. No. 5,552,882 referencedabove) for fiber Bragg gratings sensors, based upon well-establishedwavemeter concepts, allows the a priori and accurate determination ofnerve center locations and their corresponding response wavelengths. Oneconfiguration of such a tool is shown in FIG. 1.

In accordance to the operational principles outlined in U.S. Pat. No.5,552,882 as well as its reduction to practice detailed in reference. K.R. Samuel, D. R. Lyons, and G. Y. Yan, “The Realization of a BraggReflection Filter Wavemeter”, Appl. Opt., 39 (31), 5755–5761 (2000),laser light from a first laser light source is passed through a beamsplitter to create two movable divergent first laser light beams thatare reflected from a pair of mirrors so as to converge at a selectedinterference region common with that of the second set of stationarylaser light beams generated in a manner similar to that of the firstlaser light beams and common with that of all subsequent first laserlight beams generated accordingly in similar manner. The associated UVpatterns of the first laser light beams are used, upon initialcalibration, to write interference patterns into a receptor opticalfiber after being compared to the reference patterns derived from asecond laser light beams for Bragg wavelength determination. Theassociated UV patterns of the first laser light beams is used to writeinterference patterns into a receptor optical fiber after being comparedto the reference patterns of the second laser light beams for a prioriBragg wavelength determination. Furthermore, in accordance with detailedaspects of referenced U.S. Pat. No. 5,552,882, the receptor opticalfiber of the Bragg reflection filter is an optical waveguide in the formof an optical fiber but ill other aspects of referenced U.S. Pat. No.5,552,882, the optical waveguide could have other physicalconfigurations and shapes and be made of various optical materials.

The present invention exploits this metrological device by using it orsimilar devices to create thousands of nerve units similar to the threeshown in the bottom circle of the FIG. 2. These individual sensors arecapable of transferring information concerning strain (‘touchsensation’), temperature (‘heat sensation’), and other possible fieldrelated phenomena to a microprocessor unit (also depicted in the firstdiagram). The microprocessor unit, in turn, relays this same informationvia encoded electrical signals to biological nerve sites. These signalare then interpreted by the brain in a fashion similar to normal sensoryinputs that are processed through learned interpretations andcorrespondingly learned responses.

In consideration of the present invention, this patent outlines aprocess for the restoration of sensations with ‘intelligentbiomechanics’ using an existing metrological system for spatiallyregistering UV induced sensing points at locations L₁, L₁, L₁, . . .with corresponding wavelengths λ₁, λ₂, λ₃, . . . that function as nervepoints in optical fibers (see FIGS. 2 and 3).

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and attendant advantages of the present invention willbe more fully appreciated and realized as the same becomes betterunderstood when considered in combination with the accompanyingdrawings, in which referenced characters designate the same or similarparts throughout the several views, and wherein:

FIG. 1 is a diagrammatic illustration configured in accordance with theprinciples of the present invention for creating dense wavelengthdivision multiplexed nerve centers in optical fibers;

FIG. 2 is an artist conceptual view of the architectural layout of anintelligent artificial arms as described in the principles of thepresent patent, along with blow up diagrams highlighting severaldetails;

FIG. 3A is a perspective view of the nerve network of a real arm andFIG. 3B is a perspective view of a peripherally configured optical fibersensor-based artificial arm;

FIG. 4 illustrates the Dense Wavelength Division Multiplexed (DWDM)architecture for a single artificial nerve strand along with variousreadout schemes configured in accordance with the principles of thepresent invention;

FIG. 5 is a photomicrograph of a portion of an actual single grating(artificial nerve center) with a further magnified small section cutouthighlighting the index of refraction modulations (light and dark lines)that form the basis of the physical mechanisms behind the presentpatent;

FIG. 6 illustrates one possible layout configuration of the sensorarrays along the outer portions of a structure such as a human arm asdescribed in the present patent;

FIG. 7 shows the Brewster angle input fiber technique typicallyincorporated into all sensor configurations described in the presentpatent to take advantage of fiber input noise suppression as well asinput polarization selection and,

FIG. 8 illustrates the three most-likely fiber types that will be usedas artificial fiber optic nerves as outlined in the details of thepresent invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, there is shown a Bragg reflection filterwavemeter 48, configured in accordance with the principles outlined inU.S. Pat. No. 5,552,882 and reduced to practice according to Reference.K. R. Samuel, D. R. Lyons, and G. Y. Yan, “The Realization of a BraggReflection Filter Wavemeter”, Appl. Opt., 39 (31), 5755–5761 (2000), forwriting multiple, pre-registered Bragg filters in single fiber units. Inits operation, a first ultraviolet (UV) laser 10, generates a coherentfirst laser beam 14, that reflects from an angled reflector 16, thatdirects the first laser beam onto a 50% beam splitter 18. The firstlaser beam 14, is then made to diverge onto two 100% rotating mirrors20, resident on two, possibly but not necessarily, computer controlledrotating mirror mounts 40. The divergent first laser beams 14, are thenmade to converge at the same intersection region in space 22, coincidentwith both a second Reference, stationary set of laser beams 24,generated by the second laser 12. This arrangement forms a UVinterferometer, consisting of components 10, 16, 18, and 20 fordirecting an interference pattern created by the interference of thefirst laser light beams from the single laser light source 10, into acommon region defined by the image plane of the imaging optics 34 and asecond Reference interferometer, consisting of components 26, 28, 30,and 32 for directing an interference pattern created by the second,Reference, laser 12. The first interference pattern can besystematically changed, as illustrated in 42 and 44, by altering theintersection angles of the laser light forming the first laser lightbeams while keeping their intersection point in the image plane 22.Maintenance of the intersection point is accomplished by a correspondingtranslation of the stage containing the imaging optics 38, along alinear rail 50, so as to establish a constant intersection point for thefirst laser light beams 14. The holographic state of each of thesubsequent first laser light beams 14, is uniquely defined by theconstant state of the second laser light beam 24, which gives rise tothe generation a stationary holographic pattern that is subsequentlyused as a Bragg wavelength marker. These patterns 42 and 44, are thenemployed in total fringe count ratios using an oscillating dual linearphotodiode array 46, to generate electronic counts, corresponding to thefrequencies associated with the UV and Reference interference fringes,in conjunction with the calibration constant, allowing the accurateprediction of resulting Bragg wavelength is created by the first laserbeams 14. Alternately, these patterns Fourier transform rations can beused in like manner. According as to whether the interference patternsformed by the first laser beam possess low intensity in comparison tothat of the second, Reference, patterns, the insertion of an opticalmodulator 52, for phase sensitive detection and lock-in amplification,is employed.

Referring now to FIG. 2, there is shown a diagram depicting a human arm,60, with its corresponding human nerve network, and an artificial arm68, with an artificial nerve network containing typical opticalcomponents 74, consisting of preprocessed optical fiber waveguides. Inaccordance with the present patent, and in the event of a catastrophicoccurrence, the artificial arm being composed of a network ofpreprocesses optical fibers 74, allowing transmitted 64, and reflected66, light pulses carrying sensory information, can be used as areplacement of a missing or irrevocably damaged limb (an arm in thepresent example). In its implementation, the present invention consistsof individual optical fibers 74, of various compositions including butnot confirmed to Ge-doped fused silica waveguides and of variousgeometries including but not confined to the ones shown in FIG. 8,possessing multiple hundreds to thousands of holographic nerve centers76, 78, 80, etc., shown in the circular blowup of a single fiber-segmentat the bottom of FIG. 2, all registered to very high stationary-stateaccuracy, 0.01% to 0.001% error, in a priori center wavelengthdetermination, designated by λ₁, λ₂, λ₃, etc., and locationregistration, 0.5 mm to 0.1 mm, designated by L₁, L₂, L₃, etc. In afurther detailing of the concept of the present patent, an implantablecontrol box 70, containing a semiconductor laser (preferably but notnecessarily tunable) or other portable source (preferably but notnecessarily broadband), an optical fiber interface array, an integratedoptical detection array or spectral analysis system, and a low voltageelectronic multiplexing device for nerve stimulation acts as the heartof the human artificial arm interface. The final interface componentsconsisting of electrodes 62, and human nerves 72, are member-limited andboth act as single channel, multi-signal pathways for sensory feed tothe brain for final signal interpretation.

Referring to FIG. 3, we illustrate a general comparison of the human arm60, and its interior 3-dimensional nerve structures 729 to theartificial arm 68, and its peripherally oriented 2-dimensional fiberoptic nerve network 74, planned for the first generation prototypes.

Referring to FIG. 4, there is shown a typical single mode fiber opticstrain and temperature sensor array created by employing UV implantedholographic filters similar to the ones to be-used in the presentpatent. (See U.S. Pat. No. 5,191,458). In one preferred form of thepresent invention shown in FIG. 4, light sources 88 or 98, capable ofmultiple wavelength generation spanning the range of wavelength filters120, 122, . . . , 124, corresponding to Bragg filter resonancewavelength λ₁, λ₂, . . . , λ_(n), illuminate the holographic filters ofa preprocessed optical fiber 96, consisting of a cladding region 132,and a guiding core region 130. The light source 88, might consist of anarrow linewidth tunable laser while the alternate light source mightconsist of a broadband superluminescent laser diode. One or the other ofthese sources generates an illuminating transmitted beam 90 or 102, thatpasses through a beam splitter 92 or 100, respectively, that is thenfocused into the sensing fiber 96, by way of a micro-lens 94. Uponentering the fiber containing holographic index of refractionmodulations of given modulation amplitudes 128, and distinct modulationfrequencies 120, 122, . . . , and 124, within the gliding region 130 ofan optical fiber, the portions of the spectrum whose wavelength iscorresponding to twice the Bragg filter modulation spacings areback-reflected out of the input end of the fiber. The beam, composed ofonly those frequencies associated with λ₁, λ₂, . . . , λ_(n), strikesthe partial reflectors 92 and/or 100 and enters a focusing lens 104, andpasses into a spectrum analyzer 108, or onto a wavelength dispersiveelement 110, that separates the individual wavelengths λ₁, λ₂, . . . ,λ_(n), onto photodiodes 112, 114, . . . , 116 located along anelectronic array 118. As an additional noise suppression technique, theoptical fiber 96, is coated on its end with an absorptive coating 126.

Referring to FIG. 5, there is shown a photomicrograph of a superimposedimage 140, of the holographic grating pattern 144, with blown up image146, and an optical fiber image 142, for a wavelength calibrationreference.

Referring to FIG. 6, there is illustrated the fiber sensor array 158,shown to be oriented along the longitudinal axis of the artificial limbsymbolically displayed as a cylindrical tube 156.

Referring to FIG. 7, there is described a typical wedged lead-in fiber96, creating a Fabry-Perot interferometer, possessing a guiding region130, a 60% partial gold-coated reflector 168, and a 100% gold-coated end166 of a given gauge length 176. As in the case of the presentinvention, the Brewster or near Brewster angled fiber input allows theanalysis of weak optical signals by optically suppressing back reflectedinsertion noise due to the interference of the typically parallel inputfiber endface. In addition, the angled nature of the endput endmaximizes the light throughput by increasing the interaction crosssection of the guiding fiber channel while minimizing the Fresnelreflection associated with the air to glass (or other higher indexmaterial) interface. The details of the wedge are as follows: A beam178, passes through a focusing microlens 170, and splits into severalparts, including a (not necessarily) minimal Fresnel reflected beam 80and a transmitted beam. The back-reflected beams return from the sensorend, without interference with the input, and splits into at least threedominant portions. There is a strong core refracted beam 178, aninternally reflected and end face refracted weak beam 182, and a weeksecond refracted beam 182. The two important angles are the incidentinput angle 172 (defined relative to the normal vector 184), and thewedge angle 174 associated with the fiber.

Referring to FIG. 8, there is shown three fiber types that areconsidered the most probable fiber geometries for use as artificialnerves. Each has a cladding region 96, surrounding a guiding core region130. The first and most prevalent geometrical shape is the circular oneshown at the top of FIG. 8. The most preferred geometry is shouts in themiddle figure and consists of a rectangular waveguide which has neverbeen commercially available due to manufacturing and handling issues butwould allow easy holographic patterning and more sensitive arraysbecause of the smaller distances between the perturbing phenomena andthe sensing (core) regions of the fibers. An intermediate geometrycontained in the D-shaped fiber at the bottom of FIG. 8, allows easyaccess to the guiding (core) regions of the fiber for greatersensitivity along with a flat, non-planewave distorting face, but alsohas some of the same handling problems associated with the flat fiber.In addition, this fiber is difficult to obtain and is in very shortsupply. Thus, for the present invention, the commercially availablecircular fibers will most likely be used along with sensitivityenhancing mechanisms incorporated as well.

Sensor Fabrication and Evaluation

Bragg sensors are fabricated by exposing the sides of single-modeGe-doped fibers to concentrated coherent UV radiation. Multiple sensingregions are created in a single fiber by writing distinct interferencepatterns in sequential steps while translating the fiber between writingsessions. The goal is to produce spatially distinct Bragg regions andallow localized measurement of stress, strain, or temperature along agiven region of the fiber. To help perform this exposure and fabricateBragg sensors with highly accurate wavelength calibration features, aspecial device called a Bragg Reflection Filter Wavemeter is beingdeveloped. Methods of and Apparatus for Calibrating Precisely SpacedMultiple Transverse Holographic Gratings in Optical Fibers, U.S. Pat.No. 5,552,882, Sep. 3, 1996, D. R. Lyons; Z. U. Ndlela. This new deviceessentially establishes a wavelength standard for precise modulationspacing of a Bragg grating and accurately calibrates each writinglocation against a known laser standard. Each sensor is distributedalong the length of the optical fiber in referenced positions, and hashigh reflectivity whenever the optical wavelength is equal to twice thegrating spacing. Since the grating spacing is extremely responsive toexternal perturbations such as strain and temperature, changes in theseparameters cause a change in the reflectivity where these sensorspossess typical linewidths of ˜0.2 nm.

The photomicrograph shown in FIG. 5 illustrates the principal upon whichthe wavelength standard is based. The interference pattern shown is theactual writing pattern in the fiber. Its corresponding Bragg resonanceis empirically determined to high accuracy with a high-resolution laserprobe. A second pattern is then used, upon its calibration, to determinethe resonance of all subsequent interference patterns based upon dualfringe counts in a similar far field image. The hardware of thewavelength comparator (or wavelength standard) system, shown in FIG. 1,uses a standard pattern that is produced in the inertial frame of amoving interferometer and a variable writing pattern that is located inthe stationary laboratory frame. This patented device or one of similarcharacter, mentioned earlier, allows accurate wavelength markers(sensing regions) to be written in a single fiber at evenly spacedwavelengths locations.

FIG. 6 shows a fiber sensor array along the longitudinal axis of theartificial and of FIGS. 2 and 3B.

Although the signals coming from these sensors are subject to theinherent noise associated with the lead-in fiber reflections, thesesignals through suitable optical noise suppression can readily beeliminated and thus allow the characterization of perturbing phenomenon.FIG. 7 shows a completed in-line fiber optic Fabry-Perot sensoremploying optical noise suppression or near Brewster angle input. TheBragg sensors are fabricated by exposing the sides of single-modeGe-doped fibers to concentrated, coherent UV radiation. Multiple sensingregions are created in a single fiber by writing distinct interferencepatterns in sequential steps while translating the fiber between writingsessions. The aim is to produce spatially distinct Bragg regions andallow localized measurement of stress, strain, or temperature along agiven region of the fiber. To help perform this exposure and fabricateBragg sensors with highly accurate wavelength calibration features, aspecial device called a Bragg Reflection Filter Wavemeter is used. K. O.Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, “Photosensitivity inoptical fiber waveguides: Application to reflection filter fabrication”,Appl. Phys. Lett., 32 (10), pp. 647–9, 1978. This new device essentiallyestablishes a wavelength standard for precise modulation spacing of aBragg gratings and accurately calibrates each writing location against aknown laser standard. Each sensor is distributed along the length of theoptical fiber in referenced positions, and has high reflectivitywhenever the optical wavelength is equal to twice the grating spacing.Since the grating spacing is extremely responsive to externalperturbation such as strain and temperature, changes in these parameterscause a change in the reflectivity. The photomicrograph shown in FIG. 5illustrates the principal upon which the wavelength standard is based.The interference pattern shown is the actual writing pattern in thefiber. Its corresponding Bragg resonance is empirically determined tohigh accuracy with a high-resolution laser probe. A second pattern isthen used, upon its calibration, to determine the resonance of allsubsequent interference patterns based upon dual fringe counts in asimilar far field image.

Biological Receptors: the Sensory System

The perception, or understanding of external sensation by neurons occursby a three step process: 1) transduction caused by a stimulus whichcreates an action potential; 2) transmission of the data through thenervous system; and 3) interpretation of the data by the brain. Althoughthis three-step process of sensory perception cannot be separated,sensory information is gathered by neural activity. Activity at theneuron is interfaced with the surroundings via sensory receptors.Sensory receptors respond to changes in the external environment andthis information concerning the external environment (extrinsic to thecell) can cause a difference in membrane potential. These receptors areeither specialized cells at the ends of neurons, or separate cells thatinfluence the physiology of the ends of neurons. These input signalsmight come in many forms, for example pressure, temperature, light,sound and injury (damage). Regardless of the initial origin of the inputsignal, the final result is that information from the receptor is linkedto the nervous system; thus, the energy that activated the sensoryreceptor as an external stimulus, leads to a signal transductionprocess. The transduction process for all receptors involves changes inthe chemical potential of ion channels. The channels occur inspecialized cells and allow for a change in bulk flow of ions across thereceptor membrane. Any change in bulk flow rate can result in, orgenerate, a change in electrical potential. This happens because achange in ion concentration across the membrane allows for a current tobe generated from the receptor membrane to the axon. This current canthen proceed to a region where the membrane can create a potential. Incells where the receptor membrane is on a separate cell, the receptorpotential causes the release of neurotransmitters that can diffuseacross the extra cellular space between the receptor cell and the neuronand bind to specific sites to cause a graded, electrical potential inthe neuron. This electrical potential leaves the cells as a signal thatcan be “fed” into a sensory pathway (a chain of end-to-end neurons).Finally, the sensory pathway provides a mechanism by which to run thesignal from the neurons to the central nervous system and eventually tothe brain where it is recognized in the cerebral cortex.

The Control of Body Movement

The central nervous system is organized in a hierarchical arrangementwith each level having a certain task in motor functioning. Neuronsfunction in the perception of the initial stimulus. They carry theirchemical messengers along a network to the brainstem, which also forms apathway that descends into the spinal column, to influence motormovement. Ultimately, this process can be used to establish an interfaceat the truncated portion of the missing limb (or other biologicalsub-system) using specific sites that are known to be sensitive toexternal stimuli. Optical signals concerning strain levels (‘touchresponses’) can be converted into modulated electrical impulses that areencoded according to location, wavelength response, and/or signalamplitude. Although some of these signals will travel the same pathways,the decoding will be interpreted by training during the rehabilitationor training phase of a subject.

All patents and publications cited herein are incorporated herein byreference in their entirety.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A device for responding to touch discrimination, comprising an arrayof optical fibers distributed over an artificial limb providing asupporting substrate for an array of optical fibers thereon having adensity similar to that of the human body; wavelength comparatorsassociated with the optical fibers, the wave length comparatorsproviding numerous sensing locations in a single fiber strand as part ofa complete fiber optic network for mechanical actuation and sensory feedback, and a UV holographic processor connected to the optical fibersrendering the optical fibers capable of responding to touchdiscrimination and location identification.
 2. The device claim 1further including a continuous wave scanner and a readout for wavelengthmultiplexed signals in the optical fibers with UV induced nerve centers.3. The device claim 1 further including sensors fabricated andincorporated into an artificial skin of a prosthetic device forsimulation of a touch sensation allowing the creation of a more fullyfunctional substitute for a lost limb or appendage.
 4. The device claim1 further including a distributed Bragg fiber optic sensor system usingspecifically processed optical fibers capable of responding to touchdiscrimination and location identification.
 5. The device of claim 1further including a system for scanning and reading out signals inwavelength multiplexed optical fibers using holographically inducedBragg gratings.
 6. The device claim 1 further including encasementschemes for superposition of multi-sensory region fibers onto arms orother intelligent structures, and a system having an ability to respondto touch and position discrimination for a finite number of locations byhaving response through an audible computer interface connected thereto.7. The devices claim 1 wherein the array of optical fibers are evenlyspaced having multiple holographic gratings in single mode fibers. 8.The device of claim 1 further including narrow linewidth lasers as wellas spectrum analyzers for characterizing wavelengths, linewidths, andreflective of gratings to characterize an entire sensing network.
 9. Thedevice of claim 1 wherein the substrate is an artificial arm and thearray of fibers is longitudinally oriented and evenly distributed aboutthe periphery of the artificial arm to create an optical fiber sensoryWDM network with peripheral architectures.
 10. The device claim 1further including a scanning laser system, a miniature spectrumanalyzer, or a broadband superluminescent source with a miniature diodearray for providing a miniaturized optical readout.
 11. The device claim1 wherein the artificial limb is a prostheses with surface bonded orembedded fibers and an additional polymer overlay with the sensitizedfibers in the overlay, the prosthesis being covered with a skin-likematerial.
 12. The device claim 1 wherein the substrate is an intelligentstructure interfaced with a talking computer to simulate responses of ahuman host in terms of touch sensitivity and location description.